Nasal pillows with high volume bypass flow and method of using same

ABSTRACT

A fan unit which in use forms part of a gases supply unit, the gases supply unit suitable for use as part of a system for providing heated humidified gases to a user, the fan unit having a casing that has an inlet aperture and an outlet passage, the outlet passage including an exit aperture, the fan unit also including a fan which is located inside the casing and which is adapted for connection to a motor to drive rotation of the fan in use, the fan drawing gases into the casing via the inlet aperture, and forcing these gases out of the casing via the outlet passage as a gases stream, the outlet passage further including at least one bypass vent hole independent of the exit aperture and arranged at an angle to the path of the gases stream through the outlet passage.

INCORPORATION BY REFERENCE TO ANY PRIORITY APPLICATIONS

This application is a continuation of U.S. patent application Ser. No.12/742,172, which is a United States National Phase filing ofPCT/NZ2008/000307, having an international filing date of Nov. 14, 2008which was published in English on May 22, 2009 under InternationalPublication No. WO 2009/064202 which claims the priority of New Zealand563497, filed on Nov. 16, 2007. These applications are herebyincorporated herein by reference in their entireties.

Any and all applications for which a foreign or domestic priority claimis identified in the Application Data Sheet as filed with the presentapplication are hereby incorporated by reference under 37 CFR 1.57.

BACKGROUND

Field of the Invention

This invention relates to devices for providing a flow of gases at apressure above atmospheric pressure to a user for therapeutic purposes.

This invention also relates to patient interfaces for use with deviceswhich provide a gases stream at a pressure above atmospheric to a userfor therapeutic purposes.

This invention also relates to methods of using patient interfaces ofknown geometry and dimensions to provide improved real time adjustmentof the characteristics of a gases stream provided to a user fortherapeutic purposes.

This invention also relates to methods of using patient interfaces ofknown geometry and dimensions to improve the initial or in-usecharacteristics of a gases stream provided to a user for therapeuticpurposes.

Description of the Related Art

Devices or systems for providing a humidified gases flow to a patientfor therapeutic purposes are well known in the art. Systems forproviding therapy of this type, for example CPAP therapy, have astructure where gases at a pressure above atmospheric are delivered froma blower (also known as a compressor, an assisted breathing unit, a fanunit, a flow generator or a pressure generator) to a humidifier chamberdownstream from the blower, where they are heated and humidified, andthen provided to a user via a user interface. Examples of commonly usedinterfaces are:

1) a full face mask,

2) a nasal mask (covering the entire nose),

3) an oral mask sealing onto the mouth,

4) nasal pillows (a pair of conduits which provide a gases stream to auser through the users nostrils, contacting and sealing around the naresof the user),

5) a nasal cannula (a pair of narrow-bore conduits that pass into thenostrils of a user without sealing on the nares),

6) a combination of the above.

Other forms of interface can be used—for example tracheostomy fittingsor similar. However, these are less common than those listed above.

Generally, the interface is connected to an outlet of the humidifier bya flexible conduit or similar. The interface is usually held in positionon a user's head by a headgear. It is common to make at least part ofthe headgear from soft adjustable straps, for example Neoprene orsimilar.

Interfaces used with CPAP devices are provided with a leak path known asa bias flow which has the purpose of venting exhaled air to atmosphere.This prevents the patient re-breathing carbon dioxide contained in theexhaled breath. For example, the Flexifit 432 full face mask includes anumber of small holes in the shell of the mask passing from the insideto the outside to act as bias vent holes.

CPAP therapy is intended to provide a fixed-pressure or constantpressure to a user. However, in reality, it is almost impossible toprovide a fixed pressure for all flow levels. Variations on basic CPAPblowers have been introduced over time in order to address shortcomings.

For example, some blowers are adapted so as to provide VP AP™ or BiP AP®(Variable/Bilevel Positive Airway Pressure) where two levels of pressureare provided by the blower: one for inhalation (IPAP) and a, lowerpressure during exhalation (EPAP).

Ramping is possible with some blowers. This is a method used at thebeginning of a user's sleep cycle to allow the user to fall asleep moreeasily. The pressure provided by the blower at the start of a sleepcycle is lower than what is ideally required. The pressure provided bythe blower is gradually increased to the prescribed level over a periodof time, allowing the user to fall asleep before the full pressure isapplied.

A blower that provides exhalation pressure relief is adapted so thatthere is a short drop in pressure during exhalation to reduce the effortrequired by a user to exhale. This feature is known by the trade nameC-Flex® in some blowers manufactured by Respironics, and by the tradename EPR™ in the machine manufactured by ResMed.

Another disadvantage that some users can experience when using a mask astheir interface is as follows: when the user exhales against an incomingpressurized stream of gases, this can cause leaks around the edges ofthe mask as the mask partially lifts away from, or is pushed off, thesurface of a user's face. This can cause a user to wake up as gases washacross their face or jet into their eyes. It can also affect theefficiency of the treatment as not all the gas provided by the blower isreaching the user (some escapes before it reaches the user). In responseto mask leak, it is common for a user or health professional to tightenthe straps of the headgear. This can lead to the mask feelinguncomfortable for a user and with time can cause pressure sores and/orsoft-tissue abrasions at the nasal bridge. The user can in responsediscontinue their therapy, or at least be unfavorably inclined towardscontinuing.

It should also be noted that uncontrolled mask leak is undesirable and agreat deal of effort has been put into measuring and minimizing maskleak, with the preferred intention of eliminating it entirely. One wayof helping to avoid mask leak is to add a one-way or bias valve to thesystem, on or close to the mask or interface. This allows exhaled gasesto be intentionally vented to atmosphere, and helps to avoid leak aroundthe edges of a mask or other sealed interface. A mask vent is describedin U.S. Pat. No. 6,662,803. A mask vent of different design is describedin EP 1275412. Several other solutions have also been suggested. Thesecan be used either alone or for example in tandem with mask vents orother solutions. U.S. Pat. No. 6,123,074 discloses a system where themask includes a suitable exhaust port, and where pressure in thebreathing system is constantly monitored and a pressure controllerdownstream of the flow generator (between the mask and the flowgenerator) acts to maintain a constant pressure within the conduit. U.S.Pat. No. 6,526,974 discloses a CPAP device where the size of the inletto the blower or flow generator can be varied, or where the size of theinlet is automatically varied, in response to the needs of the user. Anexhalation path is provided so that the back pressure in the system islimited.

If the mask or patient interface is provided with bias vent holes, thereis always going to be some level of leakage through the vent holes. Atypical level of exhaust flow through bias vent holes in a mask is inthe region of 35 Liters per minute, at a pressure level of 10 cmH₂Oabove atmospheric pressure. This is a known level of leak and can becompensated for by adjusting the settings of the blower and thehumidifier. However, a portion of the heated, humidified gases is lost(sacrificed) before reaching the user.

In contrast, one advantage of using a nasal cannula is that all the flowis provided to the nostrils and does not vent (through bias vent holes)before reaching the nasal cavity. However, unsealed nasal cannulas havetheir own shortcomings. For example, the size of the space between thenostrils and the cannula is unknown. Therefore, the amount of leak fromaround the cannula is unknown and uncontrollable, even when the pressureat the cannula is known, and the pressure delivered to the nares isunknown or uncontrollable even if the flow delivered to the cannula isknown. Also, when using a cannula, it is impossible to avoid theentrainment of dry, unheated atmospheric air into the nostrils of auser.

Another problem encountered with unsealed high flow nasal cannula is thenoise that is generated by air flowing between the nares and the outsideof the nasal cannula. This can be especially problematic when a nearlyconstant flow is provided to the user. In this situation the flowexiting to atmosphere varies significantly as the patient exhales andinhales creating noise that varies in intensity over the breath cycle.The amount of noise is strongly dependent on the position andorientation of the cannula in nares as this affects the velocity of theexhaust (leaked) gas.

High flow nasal cannula are used to provide gas for treatment ofillnesses including COPD, CF and OSA amongst many others. It issometimes desirable to set a flow rate through the cannula that issufficient to meet the patient's maximum inspiratory demand, but whichdoes not significantly exceed that required to meet maximum inspiratorydemand. This can be difficult to achieve reliably due to the unknownresistance to flow of air passing between outside of the cannula and theinside of the nares.

For treatment of some conditions the pressure at the nares is important.For example, in the treatment of some respiratory conditions, such asCOPD, application of pressure during expiration can be beneficial. Witha non-sealing nasal cannula the amount of pressure delivered is unknownas explained previously.

Nasal pillows are a variation on the basic cannula structure which isintended to go some way toward solving the problems which areexperienced with nasal cannulas. In nasal pillows, the narrow elongatedinlet portions of the cannula are replaced with soft flexible portionswhich generally conform to the geometry of a user's nostrils, and whichflex to seal against the nares of a user in use. This helps to avoidentrainment of atmospheric air into the nostrils of a user wheninhaling. However, it can be difficult to exhale against the stream ofair provided when using nasal pillows, and uncontrolled leaks can occur.It can also be difficult to create an adequate seal against the nares ifthe user's nasal geometry is significantly different from that of thepillows.

Further disadvantages arise when attempting to measure the flow and thepressure at various points in the system. It can be difficult to relateactual measured data to the breathing cycle of a user in order tomonitor or adjust (either manually or automatically through a feedbackmechanism in the blower control circuitry) controllable systemparameters such as the fan speed (to alter flow and pressure) or theenergy provided to the heater mechanism of the humidifier (to alter thetemperature and humidity of the gases) in order to provide the mosteffective therapy. It is especially difficult to accurately assesspressure and flow e.g. in the upper airway of a user when leaks occurbetween the face or nose of the patient and the interface.

Other forms of treatment deliver a high flow of gas (dry or humidified)through an unsealed interface such as a nasal cannula. In theseapplications there is a large leak out of the nostrils around the nasalcannula. The large leak means that the pressure in the airway isrelatively low compared to CPAP treatment.

A disadvantage of the high flow nasal cannula system is that it isespecially difficult to assess the values of pressure and actual patientflow during a patient's breath because the resistance to flow for gaspassing between the cannulas and the nares can be variable depending onthe position of the cannula and shape and size of the nares.

Obstructions in some patients' airways during sleep can cause limitedairflow, leading to apnea, hypopnea, or snoring. The obstruction isoften a collapsed pharynx. The obstruction may be a partial airwayobstruction, leading to altered characteristics of the airflow. Ahypopnea is a reduction of flow that is greater than 30%, but less than90% of baseline, for a period of at least 10 seconds and which isaccompanied by oxygen desaturation greater than 4% from baseline. Anapnea is similar but airflow is reduced by greater than 90% frombaseline. Each of these conditions frequently leads to sleepdeprivation.

It is well known to treat patients suffering from sleep deprivation withpositive airway pressure therapy (“PAP”). This therapy can be ContinuousPositive Airway Pressure (“CPAP”), Variable Positive Airway Pressure(“VPAP”), Bi-level Positive Airway Pressure (“BiPAP”), or any ofnumerous other forms of respiratory therapy. The application of positivepressure to the patient's pharynx helps minimize or prevent thiscollapse. Positive airway pressure therapy is currently applied by meansof an apparatus containing a pressure source, typically a blower,through a tube to a mask, which the patient wears in bed.

It is desired to control the applied pressure. Too little pressure tendsnot to solve the problem. Too much pressure tends to cause discomfort tothe patient, such as drying out of the mouth and pharynx, as well asdifficulty in exhaling against the applied pressure. The difficulty inapplying optimum pressure is that incidents of airway obstruction comeand go through the course of a night's sleep. One solution is to try tofind an optimum pressure for a particular patient and maintain thatpressure. This method requires the patient's stay at a sleep clinic,where sleep specialists can monitor the patient's course of breathingthroughout one or more night's sleep, prescribe the appropriate pressurefor that patient, and then set the apparatus to deliver the appropriatepressure. This method is, of course, inconvenient as well as expensiveto the patient and tends to be inaccurate, as a typical patient will notsleep the same when away from familiar bedding and surroundings.

Accordingly, it is desirable to be able to adjust the applied pressurewithout requiring the patient to attend at a sleep center. Devices whichare aimed at adjusting the applied pressure automatically are generallyknown as ‘Auto adjusting Devices’. Various methods of in-homeadjustments have been considered. One method generally thought to beeffective is to monitor the patient to try to anticipate the onset of anobstructed airway, and to adjust the pressure in response. When anelevated upper airway resistance or flow obstruction is anticipated orunderway, the apparatus increases the applied pressure. When the patientreturns to normal sleep, the applied pressure is reduced. The problemthen, is to determine when a flow obstruction is occurring or is aboutto occur. It is desired to anticipate correctly in order to avoid theproblems set forth above for when too much or too little pressure isapplied.

Various methods have been proposed to solve this problem. In U.S. Pat.No. 5,107,831 to Halpern, an apparatus monitors the airflow to thepatient and posits an event of airway obstruction when the patient'sbreath fails to meet a predetermined threshold of flow rate or duration.In U.S. Pat. No. 5,134,995 to Gruenke, an apparatus monitors the airflowto the patient and analyzes the shape of the flow versus time waveform.If the shape of this waveform tends to be flattened, that is, moresimilar to a plateau than to a sinusoid, the apparatus posits an eventof airway obstruction. In U.S. Pat. No. 5,245,995 to Sullivan, anapparatus monitors the patient's sound with a microphone. If audiblesnores are detected, the apparatus posits an event of airwayobstruction. Similarly, in U.S. Pat. No. 5,953,713 to Behbehani, anapparatus measures the total pressure within an interface placed over apatient's airway and inputs frequency data in the range 100 to 150 Hzinto a neural network to determine the presence of a pharyngeal wallvibration (a snore) which, according to Behbehani, is a precursor tosleep disorder breathing.

An alternative method described in US patent US20060027234A1:Auto-titrating method and apparatus. This specification discussesobtaining information from the frequency range of zero to 25 HZ in thefrequency domain of the flow, and adjusting the pressure based on theinformation obtained.

Prior art methods have not proven totally satisfactory in controllingthe applied pressure during PAP therapy. For example, the '713 patent,by measuring in the range of 100 to 150 Hz, essentially tests forsnoring and does not measure or analyze any information concerningpartial airway obstruction, as this information is found in the lowerfrequency range 0 to 25 Hz.

It is an object of the present invention to provide a breathingassistance apparatus which goes some way to overcoming theabovementioned disadvantages or which at least provides the public orindustry with a useful choice.

SUMMARY

In a first aspect the invention may broadly be said to consist in a userinterface for use as part of a system for providing gases to a patientfor therapeutic purposes, said system of the type that includes a gasessupply conduit which in use provides a gases stream, said patient havingnares, said user interface comprising;

a substantially hollow main body, adapted for attachment to one end ofsaid conduit so that in use said gases stream from said conduit canenter said main body,

a pair of nasal pillows, fluidically connected to said main body, aportion of the outer surface of each one of said pillows adapted so thatin use each of said pillows can substantially seal against theequivalent one of said nares of said patient,

each one of said pair of nasal pillows divided into three separatepassages, each of said passages sealed from the other passages at leastwithin said pillows, the first one of said passages configured to act inuse as a gases delivery passageway and connected to said main body sothat in use gases from said conduit can pass along said first passage tosaid patient, the second one of said passages configured to act as apressure measurement duct in use, and the third one of said passagesopen to atmosphere and adapted to act as a high-flow bypass passage.

In a second aspect the invention may broadly be said to consist in auser interface for use as part of a system for providing gases to apatient for therapeutic purposes, said system of the type that includesa gases supply conduit which in use provides a gases stream, saidpatient having nares, said user interface comprising;

a substantially hollow main body, adapted for attachment to one end ofsaid conduit so that in use said gases stream from said conduit canenter said main body,

a pair of nasal pillows, fluidically connected to said main body, aportion of the outer surface of each one of said pillows adapted so thatin use each of said pillows can substantially seal against theequivalent nares of said patient,

each one of said pair of nasal pillows divided into two separatepassages, each of said passages in each pillow sealed from the other,the first one of said passages configured as a gases delivery passagewayand connected to said main body so that in use gases from said gasesstream pass along said first passage to said patient, the second one ofsaid passages open to atmosphere and adapted to act as a high-flowbypass passage.

In a third aspect the invention may broadly be said to consist in asystem for providing gases to a patient for therapeutic purposes, saidsystem including a blower unit, a humidifier unit fluidically connectedto said blower unit, a user interface, and a conduit, one end of saidconduit fluidically connected to an outlet of said humidifier, the otherend of said conduit fluidically connected to said user interface so thatin use gases from said humidifier can pass along said conduit and intosaid interface,

said user interface comprising;

a substantially hollow main body, adapted for attachment to one end ofsaid conduit so that in use said gases stream from said conduit canenter said main body,

a pair of nasal pillows, fluidically connected to said main body, aportion of the outer surface of each one of said pillows adapted so thatin use each of said pillows can substantially seal against theequivalent one of said nares of said patient,

each one of said pair of nasal pillows divided into three separatepassages, each of said passages sealed from the other passages at leastwithin said pillows, the first one of said passages configured to act inuse as a gases delivery passageway and connected to said main body sothat in use gases from said conduit can pass along said first passage tosaid patient, the second one of said passages configured to act as apressure measurement duct in use, and the third one of said passagesopen to atmosphere and adapted to act as a high-flow bypass passage.

In a fourth aspect the invention may broadly be said to consist in asystem for providing gases to a patient for therapeutic purposes, saidsystem including a blower unit, a humidifier unit fluidically connectedto said blower unit, a user interface, and a conduit, one end of saidconduit fluidically connected to an outlet of said humidifier, the otherend of said conduit fluidically connected to said user interface so thatin use gases from said humidifier can pass along said conduit and intosaid interface, said user interface comprising;

a substantially hollow main body, adapted for attachment to one end ofsaid conduit so that in use said gases stream from said conduit canenter said main body,

a pair of nasal pillows, fluidically connected to said main body, aportion of the outer surface of each one of said pillows adapted so thatin use each of said pillows can substantially seal against theequivalent nares of said patient,

each one of said pair of nasal pillows divided into two separatepassages, each of said passages in each pillow sealed from the other,the first one of said passages configured as a gases delivery passagewayand connected to said main body so that in use gases from said gasesstream pass along said first passage to said patient, the second one ofsaid passages open to atmosphere and adapted to act as a high-flowbypass passage.

In a fifth aspect the invention may broadly be said to consist in amethod of reducing the likelihood of an apnea event or a snoring eventin a user who is receiving gases from a system adapted to provide apressurized gases stream to a user through a high-flow user interface,said system including control circuitry that includes a memorycomponent, said method comprising the steps of:

a) measuring the flow rate through the system in real time,

b) increasing an output parameter provided by said system if said flowrate flattens.

In a sixth aspect the invention may broadly be said to consist in amethod of providing a gases flow to a user via a high-bypass flow nasaluser interface of known geometry and dimensions, said user interface inuse forming part of a system which provides gases at a pressure aboveatmospheric to a user, said system including a blower unit and controlcircuitry which includes control algorithms, said method comprising thesteps of:

a) using said control algorithms to calculate the resistance to flowbased on said known geometry and dimensions of said nasal interface,

b) using said control algorithms to calculate the bypass flow rate for arange of pressure and flow values suitable for providing gases therapyto said user,

c) using said control algorithms to set an initial value of eitherpressure or flow to be provided by said blower unit, based on saidcalculations in steps 1) and 2).

In a seventh aspect the invention may broadly be said to consist in amethod of real time in-use adjustment of the pressure provided to a userby a gases supply system of the type which includes a blower unit havingcontrol circuitry which includes control algorithms, and a variablespeed fan unit controlled by said control circuitry, in use said gasessupply system supplying gases for therapeutic purposes at a pressureabove atmospheric to a user via a user interface, said user interfacecomprising;

a substantially hollow main body, adapted for attachment to one end ofsaid conduit so that in use said gases stream from said conduit canenter said main body,

a pair of nasal pillows, fluidically connected to said main body, aportion of the outer surface of each one of said pillows adapted so thatin use each of said pillows can substantially seal against theequivalent one of said nares of said patient,

each one of said pair of nasal pillows divided into three separatepassages, each of said passages sealed from the other passages at leastwithin said pillows, the first one of said passages configured to act inuse as a gases delivery passageway and connected to said main body sothat in use gases from said conduit can pass along said first passage tosaid patient, the second one of said passages configured to act as apressure measurement duct in use, and the third one of said passagesopen to atmosphere and adapted to act as a high-flow bypass passage, andfurther having known geometry and dimensions, said method comprising thesteps of:

a. setting an initial value of either pressure or flow to be provided bysaid blower, and providing a stream of gases from said blower to saiduser via said user interface,

b. measuring the differential pressure between atmospheric pressure andthe pressure at said interface in use and relaying data relating to saidmeasured differential pressure value to said control circuitry,

c. measuring the flow rate provided by said blower and relaying datarelating to said measured flow rate value to said control circuitry,

d. using said control algorithms to make a calculation relating to theactual pressure in said patients airway by using said pressure data,said flow data and said known geometry and dimensions of said interface,

e. comparing said calculated actual pressure value to said initialvalue,

f. vising said control circuitry to send control signals in real time tosaid fan to increase or decrease speed so that the difference betweensaid calculated actual pressure value and said initial value isdecreased.

Preferably in said method or methods said initial value is a pressurevalue, and said calculated actual pressure value is directly compared tosaid initial pressure value.

Alternatively in said method or methods said initial value is a flowvalue and said method or methods includes the step of using said controlalgorithms to convert said initial flow value to an equivalent pressurevalue so that said calculated actual pressure value can be compared tosaid initial flow value.

Preferably said methods can be applied to a user who is receiving gasesthrough a user interface comprising;

a substantially hollow main body, adapted for attachment to one end ofsaid conduit so that in use said gases stream from said conduit canenter said main body,

a pair of nasal pillows, fluidically connected to said main body, aportion of the outer surface of each one of said pillows adapted so thatin use each of said pillows can substantially seal against theequivalent one of said nares of said patient,

each one of said pair of nasal pillows divided into three separatepassages, each of said passages sealed from the other passages at leastwithin said pillows, the first one of said passages configured to act inuse as a gases delivery passageway and connected to said main body sothat in use gases from said conduit can pass along said first passage tosaid patient, the second one of said passages configured to act as apressure measurement duct in use, and the third one of said passagesopen to atmosphere and adapted to act as a high-flow bypass passage.

Preferably said methods can be applied to a user who is receiving gasesthrough a user-interface comprising;

a substantially hollow main body, adapted for attachment to one end ofsaid conduit so that in use said gases stream from said conduit canenter said main body,

a pair of nasal pillows, fluidically connected to said main body, aportion of the outer surface of each one of said pillows adapted so thatin use each of said pillows can substantially seal against theequivalent nares of said patient,

each one of said pair of nasal pillows divided into two separatepassages, each of said passages in each pillow sealed from the other,the first one of said passages configured as a gases delivery passagewayand connected to said main body so that in use gases from said gasesstream pass along said first passage to said patient, the second one ofsaid passages open to atmosphere and adapted to act as a high-flowbypass passage.

Preferably in said methods said output parameter is pressure.

Alternatively in said methods said output parameter is flow.

Preferably said methods can be applied to a user who is receiving gasesthrough a nasal cannula.

Alternatively said methods can be applied to a user who is receivinggases through a user interface comprising;

a substantially hollow main body, adapted for attachment to one end ofsaid conduit so that in use said gases stream from said conduit canenter said main body,

a pair of nasal pillows, fluidically connected to said main body, aportion of the outer surface of each one of said pillows adapted so thatin use each of said pillows can substantially seal against theequivalent one of said nares of said patient,

each one of said pair of nasal pillows divided into three separatepassages, each of said passages sealed from the other passages at leastwithin said pillows, the first one of said passages configured to act inuse as a gases delivery passageway and connected to said main body sothat in use gases from said conduit can pass along said first passage tosaid patient, the second one of said passages configured to act as apressure measurement duct in use, and the third one of said passagesopen to atmosphere and adapted to act as a high-flow bypass passage.

Alternatively said methods can be applied to a user who is receivinggases through a user interface comprising;

a substantially hollow main body, adapted for attachment to one end ofsaid conduit so that in use said gases stream from said conduit canenter said main body,

a pair of nasal pillows, fluidically connected to said main body, aportion of the outer surface of each one of said pillows adapted so thatin use each of said pillows can substantially seal against theequivalent nares of said patient,

each one of said pair of nasal pillows divided into two separatepassages, each of said passages in each pillow sealed from the other,the first one of said passages configured as a gases delivery passagewayand connected to said main body so that in use gases from said gasesstream pass along said first passage to said patient, the second one ofsaid passages open to atmosphere and adapted to act as a high-flowbypass passage.

Preferably said third one of said passages open to atmosphereimmediately adjacent to said nares

Preferably said main body is internally divided, so that said gasesstream divides into two substantially equal portions which pass out ofsaid main body, one portion to each to each of said pillows.

Preferably said main body is further internally divided so that each ofsaid second ones of said passages merge within said main body into asingle main body pressure measurement duct, said main body pressuremeasurement duct sealed from said gases stream entering said main bodyfrom said conduit.

Preferably said patient interface further includes an interface pressuresensor, said main body pressure measurement duct fluidically connectedto said pressure measurement sensor in use.

Alternatively said patient interface further includes a pressure sensorand a tube, said pressure sensor located remotely from said main bodyand said pillows and connected to said main body pressure measuring ductby said tube.

Preferably said interface pressure sensor is a standard pressure sensor.

Alternatively said interface pressure sensor is a single differentialpressure sensor.

Preferably said user interface geometry and dimensions are chosen toprovide a fixed resistance to flow such that when a differentialpressure of 10 cmH₂O is provided to said interface in use, the flow ratethrough said high-flow bypass passage is substantially between 50 to 70Liters per minute.

Preferably each of said nasal pillows are formed from a soft rubbermaterial.

BRIEF DESCRIPTION OF THE DRAWINGS

A preferred form of the present invention will now be described withreference to the accompanying drawings.

FIG. 1 shows a schematic view of a user receiving humidified air from amodular blower/humidifier system of a known, prior art, type.

FIG. 2a shows a perspective view of the preferred embodiment of theinterface of the present invention, the interface consisting of a pairof nasal pillows attached to a main body, the main body having anattachment for head straps and an attachment adapted to receive a gasesconduit.

FIG. 2b shows a perspective view of the preferred embodiment of theinterface of the present invention attached to a headgear, with aconduit attached to provide a pressurized gases stream to the main bodyof the interface.

FIGS. 3a, b and c show schematic cross-sections of three differentpreferred forms of the nasal pillows of the present invention.

FIG. 4 shows a typical graph of flow rate (y-axis) vs time (x-axis) fora healthy user inhaling and exhaling.

FIG. 5 shows a typical graph of flow rate (y-axis) vs time (x-axis) fora user who may require breathing assistance, with abnormalities in theirbreathing cycle.

FIG. 6 shows a user end view of the nasal pillows of FIG. 2, having across-section as shown in FIG. 3 c.

FIGS. 7a, 7b and 7c show schematic cross-sections of a second preferredform of the nasal pillows of the present invention, with two separatepassages passing through the nasal pillows.

FIG. 8 shows a flow chart of the feedback process by which thecharacteristics of the gases stream delivered to a user may be adjustedin use in real time.

FIG. 9 shows a schematic view of a blower unit that forms part of thegases delivery system, showing interconnections between controlcircuitry located inside the blower unit, control algorithms containedwithin the control circuitry, inputs from sensors associated with thegases delivery system, and inputs from a user control panel, and outputsto a fan unit located inside said blower unit in response to signalssent from the control circuitry, the signals calculated using outputsfrom the control algorithms.

DETAILED DESCRIPTION

The present invention will be described with reference to a gases supplysystem 1 comprising four main parts: a blower unit 2, a humidifier unit3 connected to the blower unit 2, a patient interface 4, and a conduit 5connecting the patient interface 4 with the humidifier unit 3. In theexample system shown in FIG. 1, the humidifier unit 3 is separate to theblower unit 2 (which can also be referred to as a respirator unit orgases supply unit). Systems of this type where the humidifier unit 3 andthe blower unit 2 are separate items are usually referred to as modularsystems. Systems where the blower unit and the humidifier unit arerigidly connected can be referred to as integrated units. However, itshould be noted that the invention is equally-applicable to either amodular system (a system where the humidifier unit 3 and the blower unit2 are separate and connected by a flexible conduit or similar), or anintegrated system.

It is not necessary to describe all the details of the structure, of thesystem 1 in order to fully describe the present invention. However, itshould be noted that the primary purpose of the system 1 is to provide astream of gases to a user 6 at a pressure above atmospheric pressure,and it is preferred that these gases are heated and humidified. Thegases stream is provided to a user for therapeutic purposes—e.g. fortreating sleep apnea, snoring or similar.

As outlined above, the blower unit 2 provides a stream of air to thehumidifier unit 3, where it is heated and humidified. Ideally, thepatient receives gas at a temperature of substantially 34 degreesCelsius and a humidity of 95% (although the most acceptable range isbetween 30-37 degrees Celsius and 85-100% humidity, and it should benoted that in certain circumstances gases can be provided which falloutside this range of temperature and humidity). The patient or user 6receives the heated, humidified gases via a user interface 4, which isfluidically connected to one end of flexible conduit 5, the other end ofwhich is fluidically connected to the outlet 7 of the humidifier 3, sothat gases can pass along the conduit 5 to the user interface 4. Ifrequired, the conduit 5 can be heated to maintain the gases temperatureand humidity levels after the gases leave the humidifier.

In use, the blower unit 2 is initially set to a user-specified pressureor flow level—an initial value. A schematic layout of the blower unit 2is shown in FIG. 9, which shows a schematic view of a blower unit thatforms part of the gases delivery system. Interconnections representativeof data signals are shown between control circuitry 100 which is locatedinside the blower unit, control algorithms 101 contained within thecontrol circuitry, a pressure signal input 110 from a pressure sensor orsensors associated with the gases delivery system, inputs from a usercontrol panel 105, and output signals 106 to a fan unit 107 locatedinside the blower unit 2 are also shown. The output signals 106 are sentfrom the control circuitry 100 and are calculated using outputs from thecontrol algorithms 101. The control circuitry 100 adjusts the speed ofthe internal fan or impeller 102 within the fan unit 107 to provide theuser-requested pressure or flow level, shown as output 104. In thepreferred form, the output 104 will pass into the humidifier unit 3. Thesystem 1 also includes various sensors which measure operatingparameters of the system as follows:

The static atmospheric pressure may be measured—e.g. by means of astatic pressure sensor located at or on the blower unit 2. For example,the static pressure sensor can be on, in or recessed into the casing ofthe blower unit 2. The pressure at the interface 4 may be measured byusing an interface pressure sensor 2000 located on or in the interface4, measuring the pressure of the flow of gases provided to the interfaceby the blower. The two pressure measurements are sent to the controlcircuitry as a pressure signal input 110 as shown in FIG. 9 and comparedusing the control algorithms in order to find the differential pressure.Alternatively the interface 3000 pressure sensor can be a singledifferential pressure sensor which measures the pressure differencebetween the interface and atmospheric pressure directly, and which sendsa pressure signal input 110.

This pressure value is the value that is set by a medical professionalsuch as a clinician when they initially prescribe the pressure level fora patient. The medical professional may alternatively prescribe a flowrate for the patient or user.

Additionally, if desired the flow rate of the gases stream can bemeasured by means of a flow sensor 109 located in the blower unit 2. Itis preferred that the flow sensor is placed at a position in the systemwhere the measured flow will be reasonably constant, for example at theoutlet of the fan that is enclosed within the casing of the blower unit2, or a similar position. The flow at other locations in the system canbe disrupted by the users breathing cycle and it can therefore bedifficult to measure the flow rate accurately. That is, it can bedifficult to measure the flow rate in a manner that allows adjustmentsto fan speed to be made which are of the necessary precision so that theusers therapy regime is effectively altered on a breath-to-breath basis.A signal 111 corresponding to the measured flow is sent to the controlcircuitry.

In the preferred form as outlined above, the user interface is used aspart of a system 1 for providing a pressurized gases stream to a user,which is most preferably heated and humidified. A user sets the blowerunit 2 to an initial setting, which is a constant pressure setting. Thisinitial level can be adjusted using the control panel 105 according tothe user's needs and signal 112 is sent to the control circuitryindicative of the initial set value. For a constant pressure setting,the flow rate delivered by the blower unit 2 may vary, depending on thebreathing of the user 6. For example, the delivered flow will drop whenthe user 6 exhales. An ideal CPAP device delivers a constant pressurefor all breathing flow rates. However, in practice a constant pressurefor all flow rates is practically unachievable. Therefore, for any givenuser-set pressure, the actual pressure delivered by the blower unit 2will vary as a user inhales and exhales, and as the speed of the fan isaltered to alter the flow rate.

The preferred form of fan unit is speed adjustable, to provide a rangeof differential pressures. The usual (most common) level which is usedby the majority of users is in the region of 20 cmH₂O. However,differential pressures of between approximately 4 CmH₂O up to 60 CmH₂Ocan be used in therapy regimes.

The preferred embodiments of the user-interfaces of the presentinvention relate to two types of user interface: a sealed interface 4and an unsealed interface (not shown). These are described below.

Sealed User Interface with a High Bypass Flow

The preferred form of sealed user interface 4 is shown in FIGS. 2a and2b . The user interface 4 is intended to seal against the nares of theuser 6, and comprises a set or pair of nasal pillows 8, mounted on ahousing or main body portion 9 so that gases can freely pass between themain body 9 and the nasal pillows 8—they are fluidically connected. Itshould be noted that within the context of this specification, ‘nasalpillows’ refers to an interface which seals against the nares of a user,and ‘nasal cannula’ refers to an interface that includes prongs which donot seal against the users nares. In the preferred form, the main bodyportion 9 is connected to a headgear assembly 10 which in use holds theinterface 4 in position on the user 6. One end—the user end—of theconduit 5 is fluidically connected to the body portion so as to providea stream of heated humidified gases to each of the nasal pillows 8, withthe other end connected to the outlet of the humidifier unit 3. Thisenables a stream of heated humidified gases to be provided in use fromthe humidifier unit 3 to a user via their nose. The nasal pillows 8include, or are integrally formed as, a seal or sealing mechanism 11which seals around or against the inside of the nares of the user 6 inuse. The seal is a soft rubber or silicone flange 11 or similar.’ Theinternal cross-sectional structure of the interface 4 and the pillows 8is described in detail below with reference to FIGS. 3a, 3b and 3 c.

FIGS. 3a, 3b and 3c show a cross-section of three preferred forms of oneof the pair of nasal pillows 8 a, 8 b, 8 c (i.e. the figures show eitherthe left one or the right one of the pair of pillows—each one for eachnostril is identical to the other). As can be seen, for each of thepreferred forms, the cross-section is divided into three separate parts,portions or passages. In FIG. 3a , these are shown as three differentsectors or sections of the circle—‘slices’. In FIG. 3b , threeconcentric circles are shown, representing a concentric conduitstructure. The outer surface or edge of the pillows 8 b seals againstthe nares of the user. FIG. 3c shows the cross-sectional area of thecircle divided into three portions asymmetrically. It should be notedthat all of the examples shown are schematic representations and are notnecessarily indicative of the actual geometry of the nasal pillows 8 a,8 b, 8 c. Each of the passages is sealed from the others so that thereis no intermingling of the gases when they are in the passages.

FIG. 6 shows a user-end view of the interface 4, with the nasal pillows8 a configured so that each is divided into three ‘slices’ as describedabove and shown in FIG. 3 a.

The operating principle in each case is the same. Gases are deliveredfrom the main body 9 through a first (or delivery) one of the threepassages or sections (e.g. one of the ‘slices’ or one of the concentriccircle sections). For example, either section 12 a in FIG. 3a , section12 b in FIG. 3b , or section 12 c in FIG. 3c . Pressure is measuredthrough a second one of the three sections or passages—e.g. section 13 ain FIG. 3a , or section 13 b in FIG. 3b , or section 13 c in FIG. 3c .The third section or passage 14 a, 14 b or 14 c is adapted to allowcontrolled high-volume bypass flow or venting. That is, in the mostpreferred form a stream of heated and humidified gases are delivered tothe upper airway or nasal cavity of a user 6 via the delivery section 12a, 12 b or 12 c. When a user 6 is inhaling, the majority of thesedelivered gases will be drawn into the user's lungs. As the user 6exhales, the preferred construction allows the majority of the gases toimmediately vent to atmosphere via the vent 14 a, 14 b or 14 c, whichare located substantially immediately adjacent to the nares of the user(e.g. in use ideally not more than 5-6 mm from the patients nares, andvery preferably less than 10 mm-15 mm. When the word ‘immediately’ isused in this specification, it should be taken to mean less than 10-15mm). Alternative constructions are possible, where the vents are locatedat a distance greater than this from the nares of the user. Theconstruction should not be limited to ‘immediate’ venting unlessspecifically stated.

In the preferred form, the delivery conduit 5 is divided into twoseparate portions along its length. The first portion 4 a forms part ofthe delivery section—i.e. ending at delivery section 12 a or 12 b, andtransports heated humidified gases from the humidifier. The secondportion 4 b is used to measure the pressure and runs between the blowerunit 2 and the pressure measurement section 13 a, 13 b or 13 c.

It should also be noted that in the preferred form, the nasal pillows 8are adapted so that the vent section(s) 14 a, b or c vent to atmosphereimmediately adjacent to the nares of the patient. The two remainingsections (12 and 13) divide within the main body portion 9 so that gasesare provided into the upper airway via one section 12, which brancheswithin the body 9 so as to provide pressure to each pillow 8, andpressure is measured via the other section 13, which also divides orbranches within the body 9. That is, the main body 9 is internallydivided.

For a normal or prior art nasal cannula, with thin nasal inlet sectionssubstantially smaller than the internal cross-sectional area of theuser's nostrils, any venting or similar around the inlet sections isuncontrolled leaking. The exact nasal geometry and dimensions areunknown, and therefore the proportion of gases venting to atmospherearound the outlets of the unsealed nasal cannula is unknown andtherefore uncontrolled.

In contrast, the proportions of a sealed, high-bypass nasal pillowinterface such as the preferred embodiment described above are knownfrom the geometry and the dimensions. The bypass venting or bypass flowcan be referred to as ‘controlled leaking’. Effectively, because theresistance to flow is fixed, the relationship between pressure and flowcan be calculated.

Feedback and Adjustment Using a Sealed Interface with a High Bypass Flow

As has been described above, the nasal pillows 8 of the presentinvention allow a known amount of gas to vent or bypass at the patientinterface 4. The geometry of the patient interface 4 is fixed.Uncontrolled leaking is minimized to the point where it is effectivelyirrelevant. The system is built so as to include a bypass path withknown geometry and dimensions, which has a lower resistance by severalorders of magnitude than any uncontrolled leak path around the seal 11,and also bias vent holes such as are known in the prior art. Theresistance to flow of the interface 4 is fixed and therefore for anysize or particular variant of the construction the resistance to flowcan be calculated from the specific geometry and dimensions. As outlinedabove, the flow from the blower unit 2 is measured by means of a flowsensor. As the flow rate is known from the reading of the sensor, andthe bypass or vent path is known, accurate real time calculation of theactual pressure in the patient's upper airway or nasal cavity can beachieved by sensing the flow data and transmitting this data to controlalgorithms programmed into or located in the control circuitry of theblower unit 2. The control circuitry receives data input from the flowsensor and the pressure sensors (so the differential pressure can becalculated). As the resistance to flow is known from the geometry, thepressure in the upper airway or nasal cavity can be calculated using thecontrol algorithms. Therefore, the pressure can be adjusted asnecessary, by sending control signals to the fan so that the fan speedis adjusted to alter the pressure.

As outlined in the ‘background of the invention’ section above, highflow nasal cannula are frequently used to provide gas for treatment ofillnesses including COPD, CF and OSA amongst many others. It isdesirable to set a flow rate through the cannula that is sufficient tomeet the patient's maximum inspiratory demand, but which does notsignificantly exceed that required to meet maximum inspiratory demand.By measuring or calculating the pressure at the interface exit or naresin the manner outlined above, and ensuring that this pressure is alwaysgreater than atmospheric pressure, the flow rate can be set so that itis sufficient to meet the patient's maximum inspiratory demand, but sothat it does significantly exceed that required to meet maximuminspiratory demand. To ensure that the flow delivered is equal to thatrequired to meet maximum inspiratory demand the flow can be adjusted sothat minimum pressure at the nares/interface is approximately equal toatmospheric pressure.

By continuously monitoring pressure the flow rate can be adjusted overtime to accommodate changes in peak inspiratory demand. This can be donemanually by the user or clinician. Alternatively, this can be carriedout automatically via a feedback mechanism where the pressure, flowand/or blower speed is varied at the flow generator.

With the interface design outlined here the pressure delivered is awell-defined function of the flow exiting the exhaust section of theinterface. Furthermore in the preferred embodiment as described above,where the interface includes a passage allowing pressure measurement atthe interface or near the nares, the pressure delivered duringexpiration can be measured and adjusted. The can be done by adjustingthe pressure, flow and/or blower speed of the flow generator.Furthermore this can be done manually or, preferably, automatically.

The arrangement described above also has the advantage that it is fareasier for a patient to exhale against the incoming flow than with priorart nasal pillows where there is no flow venting directly at theinterface (nasal pillows with flow venting e.g. at an elbow connectorjust upstream of the interface are known. It is also known to add biasvent holes in a housing that is used with nasal pillows in order toprovide bias venting). As noted above, masks which include bias ventholes typically vent approximately 35 Liters per minute of exhaust flowwhen the pressure is around 10 cmH₂O above atmospheric pressure (adifferential pressure of 10 cmH₂O).

In contrast, in a system such as the one described above, the blowerunit 2 will typically provide a flow rate of between 20 Liters perminute to 60 Liters per minute (although the flow rate could also lieoutside these limits). The mask pressure to produce the required flowwill typically be in the range 0.5 to 15 cmH₂O. The resistance to flowusing the arrangement described 91 above is between two to four timesless than the equivalent in conventional masks. That is, the resistanceto flow of the bypass passage is such that the flow rate at a pressureof 10 cmH₂O will typically be 50 to 70 Liters per minute at a pressureof 10 cmH₂O.

It should be noted that the term ‘sealed’ as used in the contextdescribed above means that an effective seal is created around the naresof the patient or user 6. Clearly, due to the high bypass flow, thesystem is not effectively sealed against atmosphere. However, the bypassflow is controlled as the geometry of the interface is known. Therefore,other parameters can be accurately measured or calculated in order forthe system 1 to be effectively controlled.

It is preferred that a sealed patient interface is used, as there areadvantages in terms of patient comfort. For example: entraining ofatmospheric air is minimized; the flow rate can be effectively measured;the patient interface will not tend to be pushed off the users face asthe user exhales causing leaks and leading to discomfort; and theresistance to flow is two to four times less than with equivalent masksystems that include bias venting. Also, a general advantage of usingnasal pillows is that all of the humidified flow at the interface isdelivered into the nostril of a user. In contrast, when using e.g. anasal mask a proportion of the flow will vent (through bias vent holes)before reaching the user interface (mask). It is also preferred for thepurposes of patient comfort that the gases provided to the patient areheated and humidified. Although this is strongly preferred, it is notabsolutely necessary.

A further advantage of using a design based on sealed nasal pillows witha separate isolated leak path is that the escaping gas passing throughthe leak path can be passed to atmosphere further from the user,reducing the perceived noise. Furthermore, because the resistance of thegas exhaust section of the pillows and the geometry of the exit apertureare well defined, the noise level is reduced and consistent.

In some circumstances it can be advantageous to use a normal nasalcannula—that is, an unsealed system where the geometry is not known. Theadvantages are outlined below.

Feedback and Adjustment Using a Sealed or an Unsealed User Interface

As can be seen from a comparison of the graphs in FIGS. 4 and 5, thereis a marked difference between normal breathing and breathingcharacterized by a partial airway obstruction, all in low frequencies.The present application exploits this difference to control the deliveryof therapeutic gas. When the flow rate is measured for a breathingsystem that is used with a high-flow rate user interface, there is animprovement in the detection of abnormal flow (e.g. a flattening of theinhalation curve, potentially in combination with a lengthening of theinhalation curve, and also potentially in combination with theinhalation curve becoming jagged or spiky).

A typical graph of flow vs time for a healthy user inhaling and exhalingis shown in FIG. 4. The inhalation portion of the cycle is shown asinhalation portion 20. The user then exhales as shown in portion 21, andthere is then a pause as shown in section 22 before the cycle startsagain. As can be seen, for a healthy user, the curve is generally smoothand apart from the ‘pause’ section at 22 follows a sinusoidal pattern.

A typical graph of flow vs time for a user who may require breathingassistance is shown in FIG. 5. A potential abnormality is shown in theinhalation portion of the curve at 23, where in contrast to the curvefor the healthy user, the inhalation curve flattens. Studies have shownthat as well as flattening, the curve may also become irregular, jagged,or ridged indicating some form of upper airway resistance. In abnormalsleep breathing patterns of this type, the curve will always flatten tosome degree. It may also lengthen as well.

By measuring the flow rate through the system in real time, the pressurecan be adjusted when the onset of an abnormal sleep breathing pattern isdetected. Measurement of the flow rate with time can be carried out whenthe user is using a sealed interface such as interface 4 that includesnasal pillows 8 as described above, or when the user is receiving gasesfrom an unsealed system—for example a normal nasal cannula 104. Thecontrol circuitry of the blower unit 2 can be adapted to includealgorithms which increase the fan speed when an abnormality is detected,so that the pressure provided to a user is increased and airway patencyis maintained.

As outlined above, another advantage of using a design based on sealednasal pillows with a separate isolated leak path is that the escapinggas passing through the leak path can be passed to atmosphere furtherfrom the user, reducing the perceived noise. Furthermore, because theresistance of the gas exhaust section of the pillows and the geometry ofthe exit aperture are well defined, the noise level is reduced andconsistent.

Sealed High Bypass Nasal Gases Delivery System with No Adjustment

What has been described above is a system where the structure of thegases delivery interface allows pressure measurements to be made at theinterface to allow adjustment of the gases pressure or the gases flowprovided to a user, with the adjustment taking place in real time.

It is also possible to use a high-bypass system with known geometrywhich does not include pressure or flow adjustment.

In a system of this type the structure of the user interface isexternally very similar to that shown in FIGS. 2a and 2b . However,there is no need for an internal pressure measurement duct. Therefore incross-section, each of the pillows can be divided into two portions orpassages instead of three.

Preferred schematic cross-sections of this alternative form are shown inFIGS. 7a, 7b and 7c . In use, the gases are delivered into the nares ofa user though the gases delivery passage 20 a, 20 b or 20 c. The highbypass flow passage—either 21 a, 21 b, or 21 c is immediately adjacentto the nares of a user, in a similar fashion to that describedpreviously.

As the geometry of the nasal pillows is known, the resistance to flowcan be calculated for any given size and geometry of user interface forthe range of flow and pressures that will be used. Therefore, it iseasier to calculate (and therefore set) an initial value of flow orpressure (or an in-use value to which the flow or pressure will ramp upto). There are fewer unknown variables to take into consideration—thegeometry and dimensions are known, the flow rate or pressure rate isknown, and the bypass flow rate can be calculated from the knowngeometry/dimensions, the known resistance to flow and the known initialsetting of pressure or flow. A system of this type requires less in theway of initial and on-going adjustment for any given user. Also, alarger proportion of users will be able to adapt to gases therapyregimes in less time than would otherwise be the case.

Also, as has been outlined above, a design based on sealed nasal pillowswith a separate isolated leak path has the advantage that the escapinggas passing through the leak path can be passed to atmosphere furtherfrom the user, reducing the perceived noise. Furthermore, because theresistance of the gas exhaust section of the pillows and geometry of theexit aperture is well defined, the noise level is reduced andconsistent.

What is claimed is:
 1. A method of providing gases to an airway of apatient via a system that includes a patient interface having a pressuresensor, a gasses source configured to provide a gases stream, controlcircuitry configured to control a flow rate of said gases stream, and aconduit having first and second ends, said conduit in fluidcommunication with said gases source at said first end and in fluidcommunication with said patient interface at said second end, saidmethod comprising: receiving, by said control circuitry, a parametervalue that defines a rate at which said gases are to be provided to saidairway of said patient; determining, by said control circuitry, anairway pressure in said airway of said patient; processing, by saidcontrol circuitry, said determined airway pressure and said setparameter value to determine a pressure comparison value; and adjusting,by said control circuitry, said flow rate of said gases stream inresponse to said pressure comparison value being beyond a predeterminedthreshold.
 2. The method of claim 1, wherein adjusting said flow rate ofsaid gases stream comprises adjusting a blower speed of a variable speedblower unit.
 3. The method of claim 2, wherein adjusting the blowerspeed of the variable speed blower unit comprises transmitting, fromsaid control circuitry to said blower unit, a control signal to adjust aspeed of said blower unit so that said determined pressure comparisonvalue is decreased.
 4. The method of claim 2, wherein adjusting theblower speed comprises increasing said blower speed in response to saidpressure comparison value indicating that said determined airwaypressure is less than said set parameter value, and decreasing saidblower speed in response to said pressure comparison value indicatingthat said determined airway pressure is greater than said set parametervalue.
 5. The method of claim 1, wherein receiving the parameter valuecomprises: determining, by said control circuitry, a resistance to flowbased on a known geometry and known dimensions of said patientinterface; determining, by said control circuitry, a bypass flow rate ofsaid patient interface for a range of pressure and flow values suitablefor providing gases therapy to said patient; and determining, by saidcontrol circuitry, said parameter value based on said determinedresistance to flow and said determined bypass flow rate.
 6. The methodof claim 5, wherein determining said parameter value comprisesdetermining a pressure value.
 7. The method of claim 5, whereindetermining said parameter value comprises determining a flow rate. 8.The method of claim 1, further comprising measuring a differentialpressure between atmosphere and said airway pressure in said airway ofsaid patient.
 9. The method of claim 8, wherein measuring a differentialpressure comprises: measuring, with an atmospheric pressure sensor, anatmospheric pressure; and determining, by said control circuitry, adifference between said measured atmospheric pressure and saiddetermined airway pressure.
 10. The method of claim 8, wherein measuringa differential pressure comprises measuring, with a differentialpressure sensor in said patient interface, a differential pressurebetween atmosphere and said airway pressure in said airway of saidpatient.
 11. The method of claim 8, further comprising measuring, with aflow sensor, a flow rate of said gases stream.
 12. The method of claim11, wherein determining an airway pressure comprises processing, by saidcontrol circuitry, said measured differential pressure, said measuredflow rate, and a resistance-to-flow value based on a known geometry andknown dimensions of said patient interface.
 13. The method of claim 11,wherein determining an airway pressure comprises processing, by saidcontrol circuitry, said measured differential pressure, said measuredflow rate, and a resistance-to-flow value based on a known geometry andknown dimensions of said patient interface, said patient interfacecomprising a nasal cannula.
 14. The method of claim 11, whereindetermining, by said control circuitry, an airway pressure in saidairway of said patient comprises processing, by said control circuitry,said measured differential pressure, said measured flow rate, and aresistance-to-flow value based on a known geometry and known dimensionsof said patient interface, said patient interface comprising nasalpillows.
 15. The method of claim 11, wherein determining, by saidcontrol circuitry, an airway pressure in said airway of said patientcomprises processing, by said control circuitry, said measureddifferential pressure, said measured flow rate, and a resistance-to-flowvalue based on a known geometry and known dimensions of said patientinterface, said patient interface comprising: a substantially hollowmain body, adapted for attachment to said second end of said conduit sothat in use said gases stream from said conduit and enter said mainbody; a pair of nasal pillows, in fluid connection with said main body,a portion of an outer surface of each one of said nasal pillows adaptedso that in use each of said nasal pillows can substantially seal againsta respective one of nares of said patient; each one of said pair ofnasal pillows divided into three separate passages, each of saidpassages sealed from the other passages at least within said pillows,the first one of said passages configured to act in use as a gasesdelivery passageway and connected to said main body so that in use gasesfrom said conduit can pass along said first passage to said patient, thesecond one of said passages configured to act as a pressure measurementduct in use, and the third one of said passages open to atmosphere andadapted to act as a bypass passage, and further having known geometryand dimensions.
 16. The method of claim 11, wherein processing, by saidcontrol circuitry, said measured differential pressure, said measuredflow rate, and a resistance-to-flow value based on a known geometry andknown dimensions of said patient interface comprises providing saidknown patient interface geometry and dimensions having a fixedresistance to flow such that when a differential pressure of 10cmH₂O isprovided to said patient interface in use, a bypass flow rate through ahigh-flow bypass passage is substantially between 50 to 70 Liters perminute.
 17. A method of providing gases by a gases supply system havingcontrol circuitry, a variable speed fan unit controlled by said controlcircuitry, and a user interface having a known geometry and knowndimensions, said gases supply system supplying gases for therapeuticpurposes to a user via said user interface, said method comprising:receiving, by said control circuitry, an initial parameter value tocontrol said fan unit, said fan unit causing a stream of gases to flowto said user via said user interface; measuring, with a pressure sensorin said user interface, a differential pressure value betweenatmospheric pressure and a pressure at said user interface andtransmitting data representative of said measured differential pressurevalue to said control circuitry; measuring, with a flow sensor in fluidcommunication with said stream of gases, a flow rate value of saidstream of gases and transmitting data reflective of said measured flowrate value to said control circuitry, calculating, by said controlcircuitry, an actual pressure value in an airway of said user based onsaid measured differential pressure data, said measured flow rate data,and said known geometry and known dimensions of said interface, causingsaid control circuitry to send a control signal to said fan unit toincrease or decrease a speed of said fan unit so that said calculateddifference between said calculated actual pressure value and saidinitial parameter value is decreased.
 18. The method of claim 17,wherein receiving an initial parameter value comprises receiving apressure value, and wherein calculating an actual pressure valuecomprises comparing said measured differential pressure value with saidinitial pressure value.
 19. The method of claim 17, wherein receiving aninitial parameter value comprises receiving a flow rate value, andwherein calculating an actual pressure value comprises converting saidflow rate value to an equivalent pressure value so that said calculatedactual pressure value can be compared to said flow rate value.
 20. Asystem for providing gases to a patient having an airway and nares, saidsystem comprising: a blower unit having control circuitry and a variablespeed fan unit controlled by said control circuitry; a conduit having afirst end and a second end, said conduit in fluid communication withsaid blower unit at said first end; a user interface in fluidcommunication with said second end of said conduit, said user interfacecomprising: a substantially hollow main body, adapted for attachment tosaid second end of said conduit so that in use said gases stream fromsaid conduit and enter said main body; a pair of nasal pillows, in fluidconnection with said main body, a portion of an outer surface of eachone of said nasal pillows adapted so that in use each of said nasalpillows can substantially seal against the respective one of said naresof said patient; each one of said pair of nasal pillows divided intothree separate passages, each of said passages sealed from the otherpassages at least within said pillows, the first one of said passagesconfigured to act in use as a gases delivery passageway and connected tosaid main body so that in use gases from said conduit can pass alongsaid first passage to said patient, the second one of said passagesconfigured to act as a pressure measurement duct in use, and the thirdone of said passages open to atmosphere and adapted to act as a bypasspassage, and further having known geometry and dimensions; said controlcircuitry configured to receive a parameter value that defines aninitial rate at which said gases are to be provided to said airway ofsaid patient, said blower providing said gases stream at said initialrate from said blower through said conduit to said user via said userinterface; a pressure sensor, in said interface, configured to measure adifferential pressure value between atmospheric pressure and a pressureat said user interface in use and to transmit data indicative of saidmeasured differential pressure value to said control circuitry; a flowsensor, in said blower unit and in fluid communication with said gasesstream, said flow sensor configured to measure a flow rate value of saidgases stream provided by said blower and to transmit data indicative ofsaid measured flow rate value to said control circuitry; said controlcircuitry configured to determine an actual pressure in said patient'sairway by using said transmitted pressure data, said transmitted flowdata, and said known geometry and dimensions of said user interface;said control circuitry configured to determine a difference between saiddetermined actual pressure and said initial rate; and said controlcircuitry configured to send a control signal to said fan unit toincrease or decrease a speed of said fan unit so that said determineddifference between said calculated actual pressure and said initial rateis decreased.